Particulate matter in a motorcycle-dominated urban area: Source apportionment and cancer risk of lung deposited surface area (LDSA) concentrations

Abstract

Source-apportioned particle concentrations are necessary to properly evaluate the health impacts of air pollution. In this study, a measurement station was established at an urban roadside in northern Taiwan to the investigate lung deposited surface area (LDSA) concentration, a relevant metric for the adverse health effects of aerosol exposure, along with PM1 and equivalent black carbon (eBC) concentrations, particle number concentration (PNC), and particle size distribution (PSD). Through positive matrix factorization and multi-linear regression analysis, we attributed 57% of LDSA to traffic emissions over the entire study. During rush hour, the motorcycle fraction increased to 0.83 and LDSA (77.6 ± 9.9 µm2/cm3) and PNC (14,000 ± 2400 particles/cm3) values peaked, while 74% of LDSA was attributed to traffic. The LDSA ratio, defined as the ratio of measured LDSA to that estimated from the particle size distribution with a spherical assumption, also increased, highlighting the greater degree of fractal morphology during rush hour. The relationship between LDSA emitted by traffic and PNC yielded a higher r2 (0.92) than the r2 between traffic LDSA and eBC (0.82). Finally, the excess lifetime cancer risk linked with traffic emission was 1.56 × 10-4 (i.e. 15.6 excess cancer cases for a population of 100,000 people) based on the LDSA apportionment results.